1. Field of the Invention
This invention relates generally to apparatus for facilitating the percutaneous administration of medicaments and more specifically to an improvement to a hypodermic jet injector device whereby its construction is simplified and its capability of use with different medicaments on an interchangeable basis is enhanced.
2. Discussion of the Prior Art
A need exists for a relatively painless way to administer drugs percutaneously. For example, persons afflicted with diabetes mellitus have a need to take one or more doses of insulin daily to maintain an appropriate glycemic balance. Because of the natural aversion to injecting oneself with a hypodermic needle, patient compliance with a physician's dosage regimen has been a continuing obstacle to the management of diabetes using insulin injections.
In the 1960's, there was introduced into the market a device called a hypodermic jet injector in which an adjustable, measured dose of a medicament could be administered in the form of a fine, high-velocity jet, delivered under sufficient force so as to pass through the skin tissue without requiring a hypodermic needle. The proper use of the jet injector proved to be a relatively painless, and therefore more acceptable, way of introducing medicaments into the body tissue. When used to inject insulin, it also afforded a further advantage in that the medicament was dispersed through a greater volume of subcutaneous tissue than occurs when a bolus injection of insulin is introduced through a conventional hypodermic needle. As such, the ability of the body to absorb the insulin was quicker and produced significantly less trauma to the tissue.
U.S. Pat. Nos. 3,330,276; 3,521,633 and 3,908,651 describe the construction and mode of operation of representative prior art hypodermic jet injector devices. Each discloses an arrangement in which a nozzle member is secured to the end of a injector body, the nozzle having a relatively small diameter orifice formed in the end thereof, the orifice communicating with a bore leading through a two-way valve member to a chamber. Disposed in the chamber is a piston which, when driven by power springs, moves through the medicament chamber to drive medicament through the bore and out of the orifice in the nozzle. Each of these patents also describes the valving structure whereby medicament may be withdrawn from a supply vial and through a series of bores and the two-way valve into the medicament chamber of the injector device. Thus, when the valve is in its "fill" position and the piston is retracted, the resulting vacuum created causes the medicament to be withdrawn from the vial and to flow through the series of bores and the valve so as to fill the medicament chamber. At the same time, the power springs are compressed. Next, the valve is rotated to establish a through-path from the medicament chamber to the nozzle orifice. When the device is triggered, the power springs rapidly drive the piston or plunger forward to force the medicament out of the chamber and through the orifice.
Because of the residual amount of medicament remaining in the various passages leading from the supply vial to the medicament chamber in these prior art devices, it is not a simple matter to substitute different medicament types by removing a first vial and replacing it with a vial containing a different medicament. For example, a physician may wish to prescribe an insulin injection regimen in which a long-lasting insulin such as Ultralente (trademark of Eli Lilly Company) is prescribed as a basal dose taken once daily and supplemented at mealtimes with a regular, fast acting insulin. With this substitution of insulin types, it is essential that the passageways and chamber of the injector be void of the first type at the time that the second type is to be drawn from its vial and into the chamber. With the type of injector described in the prior art, it was not uncommon that 12 units or more of insulin be entrained in the various bores and channels used to connect the supply vial to the injector chamber following the administering of a first injection. This residual amount effectively precluded the use of a prior art injector in a regimen where different types of insulin were to be administered.
The present invention is deemed to be an improvement over the prior art. Specifically, the use of the present invention reduces the residual amount of medicament remaining in the injector following an injection to negligible amounts. Furthermore, the adoption and use of the present invention materially simplifies the mechanical construction of the injector device. That is to say, by using the present invention, it is possible to eliminate the rotatable ball valve and its associated housing, thus reducing the cost of the device.